DSP techniques are increasingly used in video applications, and particularly in television (TV) systems, because they allow the quality of the video signal to be enhanced without the need to change the current transmission standard.
Based on such techniques, a number of integrated devices are nowadays available which allow one to add to a normal TV appliance several features, for example line and field frequency doubling, noise reduction, brightness enhancement, and so on. A TV appliance equipped with such devices is referred to as an "Improved Quality TV" (IQTV).
As known, the video signal has a three-dimensional structure, having two spatial dimensions (horizontal and vertical) and a temporal dimension that conveys motion or scene change informations.
IQTV circuits acting on all three dimensions of the video signal, for example filters for scanning rate conversion, such as line frequency or field frequency doubling, require some kind of memory device. Generally, these memory devices are known under the name of field memories, due to the fact that they are capable of storing the image data related to one video field, e.g., 720*288*8 bits for the luminance signal and 360*288*2*8 bits for the chrominance signal, assuming that a 4:2:2 sampling format is adopted.
If, due to some failure in the manufacturing process, some memory cells of the field memory do not work properly, noise is added to the image. In fact, one or more pixels could be wrong and an outline would be visible in the image at the output of the field memory. Depending on the position of the defective memory cell, noise configurations like impulsive noise or salt-and-pepper noise are obtained. This kind of artifact is very annoying because the wrong pixels are always in the same position of the TV screen, causing a sort of dirty window effect. As a consequence, a field memory containing even a single defective memory cell is useless and must be discarded.
This problem is exacerbated by the fact that, thanks to the progress in integrated circuit technologies, future field memories will be only a part of a more complex integrated circuit, so that the presence of defective memory cells in the field memory will cause the refusal of the whole integrated device, with a great impact on the yield of the manufacturing process.
As known, particular error-correction coding strategies have already been developed, such as Cyclic Redundancy Check (CRC), polynomial codes and so on, but all these techniques require extra memory bits in addition to those necessary to store the video signal information. The overhead caused by the additional memory bits negatively affects the overall yield.